Telephone system.



W. W. DEAN.

TELEPHONE SYSTEM.

APPLICATION FILED 00m. 14, 1909.

Patented May 24, 1910.

ESHEETS-SHEET 1.

nllllmlllln MT/VESSES W. W. DEAN.

TELEPHONE SYSTEM.

APPLICATION FILED 001214, 1909.

Patented May 24,1910.

a snnnrs-snnm 3.. F76". 4

fivvsmrcw mLL/AM W DEA/V H's ATTO/ EA/Ey MTNESSES UNITED STATES PATENTOFFICE.

WILLIAM W. DEAN, OF ELYRIA, OHIO, ASSIGNOR TO THE DEAN ELECTRIC COMPANY,

OF ELYRIA, OHIO, A CORPORATION OF OHIO. I

TELEPHONE SYSTEM.

To. all whom it may concern:

Be it known that I, VILLIAM IV. DEAN, a citizen of the United States,residing at Elyria, in the county of Lorain and State of Ohio, haveinvented certain new and useful Improvements in Telephone Systems; and Ido hereby declare the following to be a full, clear, and exactdescription of the invention, such as will enable others skilled in theart to which it appertains to make and use the same.

My invention relates to telephone systems and more particularly to whatare commonly known as trunking systems. In such systems there are twooperators at different positions: the first, commonly known as the Aoperator, answers the call; and the second, or B operator, is notifiedby the A operator that a connection with a line under her jurisprudenceis desired. The connection is made between the apparatus under thecontrol of the A operator and the trunk and between the trunk and thecalled subscribers line. In a general way, such systems are well knownin the art.

One of my purposes is to produce a special arrangement of signalingbetween the various parties participating in these connections, and toso produce such arrangement that the information necessary to make theconnection and disconnection will be conveyed to the participants bythese signals without in any way endangering the connections being tiedup by their misunderstandings.

My invention will be best understood by reference to the followingdescription when taken in connection with the accompanying illustrationsshowing several specific e1nbodiments thereof, while its scope will bemore particularly pointed out in the appended claims.

Figure 1 is a diagrammatic illustration of the trunk circuit associatedwith the central station cord circuit and a pair of telephone lines.Figs. 2, 3, and (1 are modifications of the trunk circuit. Fig. 5 is anillustration of a Q-conductor cord circuit the use of which Icontemplate with my trunk circuits.

Referring now to the drawings, I show a subscribers line 12 on whichthere is a subscrihers station C and which terminates at the centralstation in the jacks JJ. The line signal relay and cutoff relay areshown associated with this line. At A I show a 3- Spccification ofLetters Patent.

Application filed October 14, 1909.

Patented May 24, 1910.

Serial No. 522,637.

conductor cord circuit terminating in the plugs P-P The tip relays TTand sleeve relays SS controlling the supervisory signals 8, s, areassociated with this cord circuit. The source of current B is alsoassociated with the cord circuit. A trunk circuit 56 is shown extendingfrom a ack J at the central station A to a trunk operator-s position atB and terminating in a plug P associated with the jacks of a pluralityof telephone lines. I show a disconnect signal at s and a combined guardand ringing signal at s". I show a low resistance relay 1% adapted to beconnected in circuit with a variable resistance D through the trunk andcord circuit. This relay is adapted to control the disconnect signal. Ihave endeavored to produce a disconnect signal which is under absolutecontrol of the A operator in order that should the A operator interruptthe connection between the cord and trunk before the conversation iscompleted, no action of the subscriber can prevent the disconnect signalbeing given to the B operator. At It I show a relay in the trunk circuitwhich is controlled by the called subscriber and which is adapted tocomplete a shunt around the variable resistance D for purposes to belater described. At R I show a relay which is used to control thecombined guard and ringing signal. At R I show a relay which iscontrolled by the plug P and which is adapted to control the circuits ofthe signals in the trunk. The trunk circuit is divided into two partsand these two parts are inductively connected through the repeatingcoils E and E Between these repeating coils I place condensers F and F.A plurality of signaling machines are shown at H, H H and H Asubscribers line 3l on which are the sub stations C C C and C terminatesin jacks J J at the B operators position.

The parts of my invention and the purposes thereof can be bestunderstood from a description of the operation of the system which is asfollows: Assume that a sub scriber C on the line 1-2 desires aconnection with a subscriber C on the line 84. The subscriber C removeshis receiver 0 from the hook it. A circuit is then completed frombattery B -7 armature 8 of relay O limb 1 substation set including thetransmitter c the hook h limb 2- armature 9 of relay O line relay L backto battery B This energizes the line relay L which pulls up its armature10, completing the following circuit through the line lamp B 11- -l210back to battery B This indicates to the A operator that the substation Gdesires a connection, whereupon she inserts the plug P into the jack Jof this line. A circuit is completed through the cut-off relay and thesleeve supervisory relay S as follows: battery B 7-Oring 7r -13-relayS14 back to battery. The relay O is energized attracting its armatures 8and 9, cutting off the line relay L from the line.

The relay S is energized to draw up the armature 15 which would completea circuit from ground through the supervisory lamp .9 and battery B wereit not for the fact that the substation circuit C is completed,providing a circuit through the relay T as follows: ground Gbattery Bl4coil 1617 sleeve 18192 the substation circuit-1 tip spring 20 tip ofcord 2l 22 the relay T23- to ground at G This energizes the relay Twhich pulls up its armature 24' interrupting the circuit of the lamp 8and preventing its operation. The A operator now presses her listeningkey and listens in to ascertain from the subscriber C what party isdesired. Having ascertained that he desires connection with a partywhose line terminates at the position of the B operator, she thencommunicates with the B operator over a special orderline (not shown)and informs her what party is desired and ascertains to which trunk sheshall connect her cord circuit. The A operator then inserts the plug Pinto the jack J completing a circuit through the sleeve supervisoryrelay S as follows: .ground GB 14.-25-S 26 2728 coil 29 ground at G Therelay S is energized and pulls up its armatures 30 and 31, cutting offthe test at 32 and completing a circuit through the lamp 8 as follows:ground GB 1 l2530 33 3ts to ground at G The armature 31 engaging frontcontact 35 completes a circuit through the relay T as follows: B 14t2536sleeve side 37-3839--5 lOD-R 4cl-6t23lH53l- 35T to ground G Resistance Dis great enough to prevent a flow of current sufficient to energize therelay T but insuflicient to prevent the operation of the relay R. Thelamp .9 is now lighted. The relay R operates, pulling up armature 16 tocomplete a circuit through the guard lamp s as follows: ground GB'-4t7l64819s to ground G9. The lamp 8 is lighted, inclicating to the Boperator that the connection at the A board has been made. After testingthe jack of the line, the B operator inserts the plug P into the jack J2 thereof, provided no busy signal is given. This completes a circuitthrough the relay R as follows: B 5O-R -51-5253O 5t back to battery BThe relay O is energized to cut off the line from the line relay L Therelay R is energized drawing up its armatures and 56. 55 engages thecontact 57 completing a second circuit through the lamp 8 as follows: G-B 50-555749s to ground G. The armature 56 is pulled up cutting off thetest 90 and engaging the front contact 58 for a purpose to be described.The signal 8 is now independent of the A operator and serves as aringing signal, being lighted during the ringing. The B operator nowpresses down the button which connects the signaling machine H intocircuit with the signaling device of the substation C C answers byremoving the receiver from the hook completing a low resistance acrossthe limbs 34 at the substation. This completes a circuit through therelay R in which circuit the resistance is now low enough to permit aflow of current sutficient to actuate said relay. The circuit is asfollows: B coil 60 of relay R 61 now closed contacts 58 and 56 of relayR 62 68 -6 llimb 4- substation circuit-limb 3666768.69- coil 70 of relayR back to battery B The relay R is energized and pulls up its armatures71 and 72. The armature 71 engages the front contact 73, completing ashunt about the resistance D. The flow of current in the circuit throughthe tip relay T the calling end of the cord, the jack end of the trunkand the relay R is sufficient to operate the relay T which pulls up thearmature 34L interrupting the circuit of the lamp 8 which is eX-,tinguished, indicating to the A operator that the called subscriber hasanswered. The armature 72 is pulled up, engaging front contact 74: andcompleting the fol lowing circuit through the relay R ground G battery B7Q7475R to ground at G. The relay R is energized, pulling up thearmature 49 completing a locking circuit from ground GR 76 49-57-55-50Bto ground at G This interrupts the circuit of the lamp 8 which indicatesto the B operator that the called subscriber has answered. The relay Ris now independent of the called subscriber. The subscribers C and Cconverse over the following circuit: through transmitter 0 hook h2l91S17 condenser F -7 38395 through the induction coils E and E-6867663 substation circuit at C 4l65.64-63 by means of the-inductioncoils to the other end of the trunk 64:243 -80 condenser F222120 limb 1back to the transmitter 0 When the conversation is completed, .thesubscribers return their receivers to the hooks. At the station C thesubstation circuit is interrupted, breaking the energizing circuit ofthe relay T and allowing the armature 2 1 to fall back, completing thecircuit of the lamp 3 through battery B 1415- 24 to ground. Theillumination of this lamp indicates to the A operator that thesubscriber C is through talking. The interruption of the substationcircuit at C breaks the energizing circuit of the relay R permitting thearmatures 71 and 72 to fall back. This breaks the shunt around theresistance D which is again placed in circuit of the relay T causing thedenergization thereof. The armature 34 falls back completing the circuitof the lamp 5' which lights, indicating to the A operator that thecalled subscriber has finished talking. The interruption of theconnection at 72- 74 is without avail, as the relay R is now energizedthrough its locking circuit. Having perceived the illumination of thelamp the A operator pulls out the plug P breaking the circuit of therelay R, whereupon the armature 46 falls back engaging its back contact82 and completing a circuit through the disconnect lamp .9 as follows:ground G*s"-82-4t6-48- 57 555OB to ground at G The operation of thissignal indicates to the B operator that the connection at P J has beenbroken. She then pulls out the plug P interrupting the circuit throughthe relays and R The armature 55 being thus released, breaks the circuitof the disconnect signal 8 and the locking circuit of the relay R at5557. The armature &9 now falls back, leaving the system in normalcondition.

The length of trunk lines in use varies, and I have made the resistanceD variable in order to compensate for variations in length; or, in fact,in any variations in resistance. The disconnect lamp .8 when the plug Pis inserted into the jack J is under absolute control of the A operator.

In Fig. 2 I show a modified trunk circuit in which the same lamp is usedfor giving both the guard and disconnect signal. The change in circuitconnections can be bestillustrated by describing the operation of thesystem from the energization of the low resistance relay R prior towhich the operation is the same as previously described in connectionwith the circuits of Fig. 1. When relay R is energized it attracts itsarmature 46 against the front contact, closing a circuit from ground atG-- through the lamp 8 16 front contact of armature 55- battery B toground at G The signal 5' is operated, indicating to the B operator thatthe A operator has inserted the plug into the jack J The B operator theninserts the plug P into the jack of the called line, whereupon a circuitis closed through battery B through relay R the plug and jack thecut-off relay of the called line to ground. This interrupts the circuitof the signal 8 closing a circuit through the ringing signal s asfollows: ground at Gs*- 4-957 55-B to ground. The lamp 8* remainslighted during the ringing. \Vhen the called subscriber responds,removing his receiver from the hook and closing a low resistance bridgeacross the line, the relay R is energized through the following circuit:B winding 7()61- the now closed switch 58 56-62* to tip side of thetrunk and line through the substation set sleeve side of line and trunk69 the coil (30 of relay R back to battery. The relay R draws up thearmatures 71 and 72, shunting the variable resistance D and permittingthe operation of the supervisory signal apparatus at the A position. Thearmature 72 closes a circuit through relay R as follows: ground at G-B72-75R ground at G. The armature 4:9 is attracted, breaking the circuitof the ringing signal 5* and closing a locking circuit upon itself asfollows: G- R 764:95755 B G The subscribers now converse and at thetermination of the conversation, the supervisory signals at the Aposition are operated, whereupon the A operator pulls out her plugscausing the deenergization of the relay R, the relay R having beendeenergized when the called subscriber hung up her receiver. The armature 46 drops back upon its back contact closing a circuit as follows:G s-- tG- 57 B G This causes the actuation of the signal .9 which servesnow as a disconnect signal. The B operator pulls out plug P and therelays R and R are de energized, and the system restored to normal. Itwill be seen that in this system I have also produced a disconnectsignal which is without the control of the called subscriber.

I show another modified form in Fig. 3 in which the signal 8 serves bothas a guard and disconnect signal. The circuit arrangements shown herecan best be described by a description of the operation which, beginningwith the energization of the low sistance relay R, is as follows: Therelay R being energized, pulls up the armature a6 closing the followingcircuit through the signal 8 G*B -47front contact of armature t(346-s96-5G97G This lights the lamp .9" which serves as the guard signal. TheB operator inserts the plug 1? into the jack of the called line, closinga circuit through relay R as follows: G B R"10Osleeve side of trunkthrough the cut-off relayto ground. This energizes the relay R whichpulls up its armatures 55 and 56. The circuit of the guard signal isbroken and the lamp extinguished. The trunk circuit is completed at 55101. A circuit is completed through the ringing lamp 8 as follows:ground G t9 s 1O2-5058 B G hen the called subscriber responds, the relayR is energized from the following circuit: G R 62to the tip of trunk andline-through the substation-back to sleeve of line and trunk 100R B GThe armature 72 is attracted, closing a circuit through the relay R andshunting the resistance D. The circuit through the relay R is asfollows: G 7275 R 5658B G The relay R pulls up its armature 49 breakingthe circuit of the ringing signal and locking itself. IVhen the calledsubscriber returns his receiver to the hook, relay R is deenergized,permitting the disconnect signal at the A situation to operate,whereupon the cord circuit plug is pulled out, deenergizing the relay Rand permitting the armature 4:6 to fall upon the back contact 82,completing a circuit through the signal 8 which now serves as adisconnect signal. This circuit is traced as follows: G -72824:6 s96-5658B G The B operator then disconnects the trunk and called line,whereupon the circuit through the relays R and R is interrupted and thetrunk restored to normal condition. In this modification I have shown asystem in which the disconnect signal is within the control of thecalled subscriber.

In Fig. 4 I show still another modification. The lamp 8 serves as both aguard and disconnect signal. Beginning with the energization of the lowresistance relay R, the operation of this system is as follows: Thearmature 46 is attracted, closing a circuit from G through s -469O56 B-G This gives the guard signal at 8 and the B operator plugs into thecalled line. The plug completes a circuit from G* through B 100sleeveside of trunk cutoff relay to ground, energizing R and completing thetrunk at 5557. The armature 56 is attracted, breaking the circuit of theguard signal and completing a circuit through the ringing signal s495856 battery 13 ground G When the called subscriber responds, acircuit is completed through R from ground G 62tip side of trunk andlinesubstation circuitsleeve side of line and trunk-100--R B -ground atG The armature 71 is attracted, shunting the resistance D, and thearmature 72 is attracted placing battery on the relay R from G, throughB 727 l 75R'-ground at G. The relay R breaks the ringing signal circuitand locks itself on the battery B When the called subscriber hangs upher receiver, the relay R is denergized breaking the shunt about theresistance D and giving the disconnect signal at the A situation. The Aoperator takes down the connection, whereupon the relay R lets go itsarmature 46 and a disconnect sig nal circuit is closed from 8 asfollows: G s 4t65856battery B G This gives the disconnect signal and theB operator proceeds to take down the connection, restoring the system tonormal.

In Fig. 5 I show a 2-conductor cord circuit which I may use with thetrunk cir cuits in place of the S-conductor cord shown in Fig. 1. Thiscircuit is well known in the art and needs no description other than tostate that the sleeve of the plug is long enough to engage both thesleeve spring 39 and the ring 28. The supervisory sleeve relays are thenoperated directly over the contacting spring. The batteries B shown inFigs. 3, l, and 5 are supplementary batteries used for signaling orother purposes, but do not constitute an essential part of thisinvention.

In all the trunk circuits shown the relay It is of low resistance, theresistance D being made high and preferably non-inductive. I may alsomake this a variable resistance. I have found this arrangement ofseparating the relay and the resistance to be of commercial advantage inthat I do away with the induction of a high wound relay and substitute acheaper, more convenient ohmic resistance which serves all the purposesof a high wound relay and which has the advantage of permitting thecontinued use of the relay R during the operation of the trunk. I regardthis feature as being prob ably the essential feature of my invention,although I do not wish to be limited to this one feature, butcontemplate claiming all the novel features of my improved system. Iintend to use this arrangement of a low resistance relay and anon-inductive resistance in any and all trunk circuits of this generalform, and regard such use as within the scope of my invention andclaims. I have shown this particular arrangement of trunk circuitssimply for the purpose of illustrating my invention and not with theintention of limiting its use thereto.

I claim:

1. In a telephone system, a plurality of subscribers lines, a centralstation circuit, a. trunk circuit adapted to be connected at one end tosaid central station circuit and at the other end to a subscriberscircuit, a supervisory relay in said central station circuit, a lowresistance relay and a high resistance in said trunk circuit adapted tobe connected in circuit with said supervisory relay when said centralcircuit is connected with the trunk circuit, said high resistancepreventing the operation of said supervisory relay, and means foreliminating said high resistance when the called subscriber responds,permitting the operation of said supervisory relay.

2. In atelephone system, a plurality of subscribers lines, a centralstation circuit, a trunk circuit adapted to be connected at one end tosaid central station circuit and at the other end to a subscriberscircuit, a

supervisory relay in said central station circuit, a low resistancerelay and a high noninductive resistance in said trunk circuit adaptedto be connected in circuit with said supervisory relay when said centralcircuit is connected with the trunk circuit, said high resistancepreventing the operation of said supervisory relay, and means foreliminating said high resistance when the called subscriber responds,permitting the operation of said supervisory relay.

3. In a telephone system, a plurality of subscribers lines, a centralstation circuit, a trunk circuit adapted to be connected at one end tosaid central station circuit and at the other end to a subscriberscircuit, a siupeiyisory relay in said central station circuit, a lowresistance relay and a high noninductive resistance in series in saidtrunk circuit adapted to be connected in circuit .with said supervisoryrelay when said central circuit is connected with the trunk circuit,said high resistance preventing the op eration of said supervisoryrelay, and means for eliminating said high resistance when the calledsubscriber responds, permitting the operation of said supervisory relay.

4. In a telephone system, a plurality of subscribers lines, acentralstation circuit, a trunk circuit adapted to be connected at oneend to said central station circuit and at the other end to asubscribers circuit, a supervisory relay in said central stationcircuit, a low resistance relay and a high non-inductive resistance insaid trunk circuit adapted to be connected in circuitwith saidsupervisory relay when said central circuit is connected with the trunkcircuit, said high resistance preventing the operation of saidsupervisory relay, and means for shunting said high resistance when thecalled subscriber responds, permitting the operation of said supervisoryrelay.

5. In a telephone system, a plurality of subscribers lines, a centralstation circuit, a trunk circuit adapted to be connected at one end tosaid central station circuit and at the other end to a subscriberscircuit, a supervisory relay in said central station circuit, a lowresistance relay and ahighnon-inductive resistance in said trunk circuitadapted to be connected in circuit with said supervisory relay when saidcentral circuit is connected with the trunk circuit, said highresistance preventing the operation of said supervisory relay, and arelay for shunting said high resistance when the called subscriberresponds, permitting the operation of said supervisory relay.

6. In a telephone system, a plurality of subscribers lines, a centralstation circuit, a trunk circuit adapted to be connected at one end tosaid central station circuit and at the other end to a subscribers line,a supervisory relay in said central station circuit, a low resistancerelay in said trunk circuit adapted to be connected in circuit with saidsupervisory relay, a signal in the trunk circuit controlled by the lowresistance relay, a non-inductive resistance in circuit with the lowresistance relay adapted to be connected in circuit with the supervisoryrelay when the trunk and central station circuits are connected, saidresistance preventing the operation of the.

supervisory relay, and a relay in the trunk circuit adapted to eliminatesaid high resistance when the called subscriber responds whereby thesupervisory relay operates.

7. In a telephone system, a plurality of subscribers lines, a centralstation circuit, a trunk circuit adapted to be connected at one end tosaid central station circuit and at the other end to a subscribers line,a supervisory relay in said central station circuit, a low resistancerelay in said trunk circuit adapted to be connected in circuit with saidsupervisory relay, a signal in the trunk circuit controlled by the lowresistance relay, a noninductive resistance in series circuit with thelow resistance relay adapted to be con nected in circuit with thesupervisory relay when the trunk and central station circuits areconnected, said resistance preventing the operation of the supervisoryrelay, and a relay in the trunk circuit adapted to eli1ninate said highresistance when the called subscriber responds whereby the supervisoryrelay operates.

8. In a telephone system, a plurality of subscribers lines, a centralstation circuit, a trunk circuit adapted to be connected at one end tosaid central station circuit and at the other end to a subscribers line,a supervisory relay in said central station circuit, a low resistancerelay in said trunk circuit adapted to be connected in circuit with saidsupervisory relay, a signal in the trunk circuit controlled by the lowresistance relay, a noninductive resistance in circuit with the lowresistance relay adapted to be connected in circuit with the supervisoryrelay when the trunk and central station circuits are connected, saidresistance preventing the operation of the supervisory relay, and arelay in the trunk circuit adapted to shunt said high resistance whenthe called subscriber responds whereby the supervisory relay operates.

99111 a telephone system, a plurality of subscribers lines, a centralstation circuit, a trunk circuit adapted to be connected at one end tosaid central station circuit and at the other end to a subscribers line,a supervisory relay in said central station circuit, a low resistancerelay in said trunk circuit adapted to be connected in circuit with saidsupervisory relay, a signal in the trunk circuit controlled by the lowresistance relay, a non-inductive resistance in series circuit with thelow resistance relay adapted to be connected in circuit with thesupervisory relay when the trunk and central station circuits areconnected, said resistance preventing the operation of the supervisoryrelay, and a relay in the trunk circuit adapted to shunt said highresistance when the called subscriber responds whereby the supervisoryrelay operates.

10. In a telephone system, a plurality of subscribers lines, a centralstation circuit a trunk circuit adapted to be connected at one endtosaid central station circuit and at the other end to a subscribers line,a supervisory relay in said central station circuit, a low resistancerelay in said trunk circuit adapted to be connected in circuit with saidsupervisory relay, a signal in the trunk circuit controlled by the lowresistance relay,

a non-inductive resistance in circuit with the low resistance relayadapted to be connected in circuit with the supervisory relay when thetrunk and central station circuits are connected, said resistancepreventing the flow of sufficient current to operate the supervisoryrelay, and a relay in the trunk circuit adapted to eliminate said highresistance when the called subscriber responds, whereby sufiicientcurrent flows through the supervisory relay to operate the same.

11. In a telephone system, a plurality of subscribers lines, a centralstation circuit, a trunk circuit adapted to be connected at one end tosaid central station circuit and at the other end to a subscribers line,a supervisory relay in said central station circuit, a low resistancerelay in said trunk circuit adapted to be connected in circuit with saidsupervisory relay, a signal in the trunk cir cuit controlled by the lowresistance relay, a non-inductive resistance in circuit with the lowresistance relay adapted to be connected in circuit with the supervisoryrelay when the trunk and central station circuits are connected, saidresistance normally preventing the flow of suflicient current to operatethe supervisory relay, a normally open shunt about said high resistance,a relay in the trunk circuit controlled over a subscribers circuit toclose said shunt whereupon sufiicient current flows to operate saidsupervisory relay.

12. In a telephone system, a plurality of subscribers lines, a centralstation circuit, a trunk circuit adapted to be connected at one end tosaid central station circuit and at the other end to a subscribers line,a supervisory relay in said central station circuit, a low resistancerelay in said trunk circuit adapted to be connected in circuit with saidsupervisory relay, a signal in the trunk circuit controlled by the lowresistance relay, a non-inductive resistance in series circuit with thelow resistance relay adapted to be connected in circuit with thesupervisory relay when the trunk and central station circuits areconnected, said resistance normally preventing the flow of sufiicientcurrent to operate the supervisory relay, a normally open shunt aboutsaid high resistance, a relay in the trunk circuit controlled over asubscribers circuit to close said shunt whereupon suflicient currentflows to operate said supervisory relay.

13. In a telephone system, a plurality of subscribers lines, a centralstation circuit, a trunk circuit adapted to be connected to said centralstation circuit and one of said subscribers lines, switches foreflecting said connections, a supervisory signal in thecentral stationcircuit, a low resistance relay in said trunk circuit, a combinationguard and disconnect signal controlled by said low resistance relay,said signal operated when one only of said connections is made andeliminated when neither or both is made, a high non-inductive resistancein circuit with the low resistance relay adapted to prevent theoperation of said supervisory relay when connected in circuit therewith,a relay controlled by the called subscriber to elimi nate saidresistance whereby said supervisory relay is operated substantially asdescribed.

14. In a telephone system, a plurality of subscribers lines, a centralstation circuit, a trunk circuit adapted to be connected to said centralstation circuit and one of said subscribers lines, switching mechanismto eftect said connections, a supervisory relay in said central stationcircuit, a high non-inductive resistance in the trunk circuit adapted tobe connected in circuit with said supervisory relay when connection ismade be tween the central station circuit and the trunk circuit and toprevent the operation of said relay when so connected, a low resistancerelay in circuit with the non-inductive resistance and the supervisoryrelay responsive to the current flow when in said circuit, a signal inthe trunk circuit controlled by said low resistance relay to-indicatethe con nection between said central and trunk circuits, said signaladapted to be eliminated when both connections to said trunk circuit aremade and to be operated again when the first connection is interruptedand thesec- 0nd remains, a third relay in said trunk controlled by thecalled subscriber and adapted when the called subscriber responds toshunt said high resistance to permit a current flow sufficient tooperate said supervisory relay.

15. In a telephone system, a plurality of subscribers lines, a centralstation circuit, a trunk circuit adapted to be connect-ed to saidcentral station circuit and one of said subscribers lines, switchingmechanism to effect said connections, a supervisory relay in saidcentral station circuit, a high non-inductive resistance in the trunkcircuit adapted to be connected in circuit with said supervisory relaywhen connection is made between the central station circuit and thetrunk circuit and to prevent the operation of said relay when soconnected, a low resistance relay in circuit with the non-inductiveresistance and the supervisory relay responsive to the current flow whenin said circuit, a signal in the trunk circuit, two circuits in whichsaid signal is located, a switch for connecting said signal in one ofsaid circuits controlled by said low resistance relay to cause actuationof said signal when the connection between the central station circuitand the trunk is completed, a fourth relay in said trunk circuitcontrolling the second circuit of said signal and adapted to elilninatesaidsignal when the trunk is connected to both the central stationcircuit and the subscribers line, both said last named relays adapted tomake connections in said circuits when the central station circuit isdisconnected from the trunk and the subscribers circuit is connectedthereto whereby said signal is again actuated, a third relay in thetrunk circuit adapted to be oper ated when the called subscriberresponds to shunt said high resistance to permit a flow of currentsu'tiicient to actuate said supervisory relay.

16, In a telephone system, a plurality of subscribers lines, a centralstation circuit, a trunk circuit adapted to be connected to said centralstation circuit and one of said subscribers lines, switching mechanismto effect said connections, a supervisory relay in said central stationcircuit, a high non-inductive resistance in the trunk circuit adapt edto be connected in circuit with said supervisory relay when connectionis made between the central station circuit and the trunk circuit and toprevent the operation of said relay when so connected, a low resistancerelay in circuit with the non-inductive resistance and the supervisoryrelay responsive to the current flow when in said circuit, a signal insaid trunk circuit controlled by said low resistance relay and adaptedto be actuated when the trunk circuit is connected to the subscribersline and disconnected from the central station circuit, a third relayadapted to be actuated when the called subscriber responds to shunt saidhigh resistanee whereupon the flow of current is suflicient to operatesaid supervisory relay.

1?. In a telephone system, a plurality of subscribers lines, a centralstation circuit, a trunk circuit connecting means for connecting asubscribers line and said central station circuit to said trunk circuit,a supervisory relay in said central station circuit, a low resistancerelay and a high non-inductive resistance in said trunk circuit arrangedto be connected in a circuit with said supervisory relay when thecentral station circuit and the trunk are connected together, said highresistance obstructing the flow of current suiiicient to prevent theoperation of the supervisory relay when so connected but permittingsutlicient flow to operate the low resistance relay, a signal insaidtrunk circuit controlled by said low resistance relay and adapted tobe operated to indicate the disconnection be tween central circuit andtrunk, and a third relay controlled by the called subscriber toeliminate said high resistance when said called subscriber respondswhereby su'liicient current flows in said supervisory relay circuit tooperate said supervisory relay.

18. In a telephone system, a plurality of subscribers lines, a centralstation circuit, a trunk circuit, circuit connecting devices adapted toconnect said trunk circuit to said central station circuit and to asubscribei"s line, a supervisory relay in said central circuit, a highnon-inductive resistance in the trunk adapted to be connected in circuitwith the supervisory relay when the central circuit and the trunkcircuits are connected and by its resistance to impede the flow ofcurrent sufficient to prevent the operation of said supervisory relay, arelay in the trunk circuit controlled by the called subscriber toeliminate said high resistance from said supervisory relay circuitwhereby sutlicient current flows therein to operate said super visoryrelay.

19. In a telephone system, a plurality of subscribers lines, a centralstation circuit, a trunk circuit, circuit connecting devices adapted toconnect said trunk circuit to said central station circuit and to asubscribers line, a supervisory relay in said central circuit, a highnon-inductive resistance in the trunk adapted to be connected in circuitwith the supervisory relay when the central circuit and the trunkcircuit are connected and by its resistance to impede the flow ofcurrent sufficient to prevent the operation of said supervisory relay, arelay in the trunk circuit controlled by the called subscriber to shuntsaid high resistance whereby sufficient current flows in saidsupervisory relay circuit to operate said supervisory relay.

20. In a telephone system, a plurality of subscribers lines, a centralstation circuit, a trunkcircuit,circuit connecting devices adapted toconnect said trunk circuit to said central station circuit and to asubscribers line, a supervisory signal in said central station circuit,a relay controlling said signal in said central circuit, a highnon-inductive resistance in said trunk circuit adapted to be connectedin circuit with said supervisory relay when said trunk and centralcircuit are united to prevent flow of sufficient current to operate saidrelay, a shunt of said high resistance and a relay controlled by thecalled subscriber to close said shunt when said called subscriberresponds whereupon suiiicient current flows in said supervisory relaycircuit to operate said supervisory relay to extinguish the supervisorysignal.

21. In a telephone system, a plurality of subscribers lines, a centralstation circuit, a trunk circuit adapted to be connected at one end tosaid central station circuit and at the other end to a subscribers line,a supervisory relay in said central station circuit, a relay and avariable resistance in said trunk circuit adapted to be connected incircuit with said supervisory relay when said central circuit isconnected with the trunk, said variable resistance being great enough toprevent sufficient currentflow to operate said supervisory relay, andmeans for eliminating said resistance when the called subscriberresponds whereupon sutficient current flows to operate the supervisoryrelay.

22. In a telephone system, a plurality of subscribers lines, a centralstation circuit, a trunk circuit adapted to be connected to the centralstation circuit and a subscribers line, a supervisory relay in thecentral station circuit, a relay, and a variable non-' inductiveresistance in said trunk circuit adapted to be connected in circuit withsaid supervisory relay when the central station circuit and the trunkare connected, said resistance preventing current flow sufficient tooperate said supervisory relay, and a third relay in the trunk circuitcont-rolled by the called subscriber and operated on his response toshunt said resistance whereby sufficient current flows to actuate thesupervisory relay.

23. In a telephone system, a plurality of subscribers lines, a centralstation circuit, a trunk circuit adapted to be connected with saidcentral station circuit and a subscribers line, a signal in the centralstation circuit controlled by current flowing over the trunk circuitwhen the central station circuit and the trunk are connected, a lowresistance relay and a high non-inductive resistance in the trunkadapted to be placed in the path of the signal controlling current whensaid connection between trunk and central circuit is made and a relaycontrolled by the called subscriber to eliminate said high resistancefrom the signal controlling circuit to change the condition of saidsignal.

24. In a telephone system, a plurality of subscribers lines, a centralstation circuit, a trunk circuit adapted to be connected with thecentral station circuit and a subscribers line, a signal in the centralstation circuit adapted to assume either an operative or inoperativecondition, a circuit formed when said trunk and central circuit areunited over which said signal is controlled, a low resistance relay anda high non-inductive resistance in said trunk adapted to be connected insaid signal controlling circuit when the trunk and central circuit areunited, a second signal located in the trunk and controlled by the lowresistance relay, a second relay located in the trunk and controlled bythe called subscriber to eliminate said high resistance from said signalcontrolling circuit whereby sufiicient current flows therein to changethe condition of said signal.

25. In a telephone system, a plurality of subscribers lines, a centralstation circuit, a trunk circuit adapted to be connected with thecentral station circuit and a subscribers line, a signal in the centralstation circuit adapted to assume either an operative or inoperativecondition, a circuit formed when said trunk and central circuit areunited over which said signal is controlled, a low resistance relay anda high non-inductive resistance in said trunk adapted to be connected insaid signal controlling circuit when the trunk and central circuitareunited, a second signal located in the trunk and controlled by the lowresistance relay, a second relay located in the trunk and controlled bythe called subscriber to shunt said high resistance from said signalcontrolling circuit whereby sufficient current flows therein to changethe condition of said signal.

26. In a telephone system, a plurality of subscribers lines, a centralstation circuit, a trunk circuit adapted to be connected with thecentral station circuitand a subscribers line, a signal in the centralstation circuit adapted to assume either an operative or inoperativecondition, a circuit formed when said trunk and central circuit areunited over which said signal is controlled, a low resistance relay anda high non-inductive resistance in series in said trunk adapted to beconnected in said signal controlling circuit when the trunk and centralcircuit are united, a second signal located in the trunk and controlledby the low resistance relay, a second relay located in the trunk andcontrolled by the called subscriber to shunt said high resistance fromsaid signal controlling circuit whereby suflicient current flows thereinto change the condition of said signal.

In testimony whereof I aflix my signature in presence of two witnesses.

WILLIAM W. DEAN.

Witnesses:

A. D. T. LIBBY, F. O. RIcI-InY.

